Yeah, if you have troubles with the amount of channels it surely is a good thing to get rid of the "echo-channels", but sometimes it can't hurt to use them (if you have channels left over) - you can have some nice effects with that echo not only in the midi, but in the spc as well. ;)
In other news I finally found out what you can do with the "l16/l8/lwhatever"-command. :p I hope this isn't some obvious information, but besides the japanese tracks no one here made use of this command so far, so I think it's new information here:
"l" set the default note lenght, which was actually explained in the japanese tutorial but there was never an example of it of what you could do with it. I noticed that S.N.N. was putting it in all of his songs so I tried one time the same and it doesn't affected anything and actually it has no use at all in S.N.N.'s tracks so far (unless I overlooked something) :p
So here how to use it:
You can put this command in the header (I guess it affect all channels that way) or in the channel you want it to have. You can also change the default note lenght per channel which can be also useful. So, if you have many notes in a channel with the lenght of 16 (like a16c16r16 and so on) you can put l16 at the channel's start and after that you can change a16c16r16 to acr.
I just tried that method out on one of my older tracks, Aquatic Ambiance, because there were many oppurtunities to use this command and because it was one of my biggest tracks so far with 3,72kb. Now it's only 2,16kb.
Here you can take a look on the updated version. Channel 0 & 3 have both the default lenght set to 16, while 1 and 2 start with l32 and change later into l16. And yeah, it's still all woking fine - the song itself is the same.
So overall the "l"-command is like the loop and "."-command a simple way to decrease the file size, which makes it much easier to use all possible slots, because you can shrink the txt-files down a lot with all that.